1. Field of the Invention
The invention relates to a method for actuating a xe2x80x9csteer-by-wirexe2x80x9d steering drive mechanism by means of at least two triggerable control motors and gear units downstream of them, by which a gear element, connected to the wheels, can be driven simultaneously.
2. Description of the Prior Art
In steer-by-wire steering drive mechanisms, either a so-called mechanical fallback plane or redundant control motors are needed. The mechanical fallback plane can be achieved for instance by a direct transmission of force from the steering wheel to the wheels to be steered if the control motors should fail. In the case of redundant control motors, some of these motors can take on the task of the others in emergencies. A steer-by-wire drive mechanism that has redundant control motors is taught for instance by U.S. Pat. No. 4,741,409, which describes single-wheel control.
As in all steering systems, even in such steer-by-wire steering drive mechanisms any steering play that occurs is problematic.
The object of the invention is therefore to refine a generic method for actuating a xe2x80x9csteer-by-wirexe2x80x9d steering drive mechanism in such a way that any steering play that may occur is maximally avoided, while producing as little irritating noise as possible.
In a method for actuating a steer-by-wire steering drive mechanism of the type defined at the outset, the above object is attained in that the two control motors can be triggered independently of one another in such away that by them both, drive forces in both the same direction and opposite directions and of equal or different amounts oriented in both the same and in opposite directions can be generated simultaneously.
Because of the capability of triggering the two control motors independently of one another in such a way that they simultaneously generate drive forces in the same direction or in particular in opposite directions of equal or different amounts, it is made possible and in an especially advantageous way that on the one hand the play is compensated for continuously by the generation of oppositely oriented drive forces. On the other hand, even high steering angle forces can be generated by drive forces in the same direction, which are required in particular in extreme situations.
The control motors are triggered such that they generate forces or drive moments in the same direction, if a customarily high steering force has to be exerted, then the two control motors are preferably triggered.
To achieve the most optimal possible compensation for the steering play, it is advantageously provided that the motors are triggered such that in normal operation, a steering angle in one direction is brought about only by actuation of one control motor, while simultaneously with this an actuation of the other control motor in the opposite direction is effected to generate a defined braking moment or a defined braking force. In this way, the entire steering drive mechanism is tensed somewhat, which highly effectively prevents any steering play.
To enable adapting the braking moment or braking force to different steering requirements, resulting in particular from different driving or road conditions and the like, it is advantageously provided that the magnitude of the braking moment or of the braking force is variable.
In another highly advantageous embodiment, the braking moment or the braking force is adjusted such that over all the steering angles, a constant difference in the drive forces generated by the two control motors ensues. Because of this difference in drive forces, which represents a tensing force, continuous tensing of the steering drive mechanism is made possible during normal operation.
To improve this tensing still further and in particular also to prevent play during very rapid adjusting motions, in an advantageous embodiment it is provided that superimposed on the forces generated by the two control motors, each of the forces having an opposite sign, is a force component that is proportional to the differential rpm of the control motors. As a result, differential vibrations of the motors, which can arise from elasticities in components of the motors and of the gear units, are in particular damped highly effectively.
Purely in principle, the most various motors can be used as the control motors. Hydraulic motors, for instance, are conceivable. Advantageously, electric motors are used as the control motors.